Recently, malfunctions of medical equipment, computer-controlled electronic precision devices, and the like as well as unintentional sudden accelerations and the like by drives of electric automobiles and hybrid automobiles have been considered as problems. Those problems are considered to be based on the existence of electromagnetic noises in the environment where the medical equipment, computer-controlled electronic precision devices, and the like are placed or in the environment where electric automobiles and hybrid automobiles are travelling.
In the meantime, noise failure is not necessarily generated in the places where the medical equipment, computer-controlled electronic precision devices, and the like are placed, even though there is a large electromagnetic field of the electromagnetic noise. It is because there is such state where noise failure is not generated in the medical equipment, computer-controlled electronic precision devices, and the like, even though there is a large electromagnetic field of the electromagnetic noise by an inverter power supply and the like that are actually closely placed under the environment where the medical equipment, computer-controlled electronic precision devices, and the like are placed. Therefore, it is considered that the noise failure is generated due to multiple factors such as the frequency and the size of the noise current flown in wiring conductors in the periphery of the electronic device, a wiring configuration of the medical equipment, computer-controlled electronic precision devices, and the like.
Currently, the problems of the noise failure generated due to the electromagnetic waves are the important interference issue to be dealt with for the medical equipment, computer-controlled electronic precision devices, and the like. Thus, various types of noise countermeasure products are developed and put on the market. However, the selection and method of use various types of noise countermeasure products and generation of the noise failure reduction effects thereof actually depend on the technical discretion of those in charge of the technology in the manufactures of the medical equipment, computer-controlled electronic precision devices that use the noise countermeasure products.
Next, modes of the electromagnetic noise current will be described.
The modes of the electromagnetic noise current inducing noise failure are generally classified into a normal mode (or a differential mode current) and a common mode current (or an unbalanced current). A phenomenon where the common mode noise current and the normal mode noise current are both superimposed on a formal signal current of a signal transmission conductor wire connected to an electronic device is well known.
Therefore, the currently-used filters are structured to deal with the noise current of both the normal and common modes. In general, the electromagnetic noise interference in the medical equipment and the computer-controlled electronic precision devices is considered to be generated mainly via a power supply line and an earth lines connected to a power lines, so that power-supply line noise filters are put on the market and used frequently. Further, while there is no normal mode noise current with a single-line earth line, it is not allowed to insert, into a line, a noise countermeasure product that obstructs the safe function that is the original function of the earth line for use. Thus, the countermeasure product thereof is limited in terms of its function.
In the meantime, the basic form of the power-supply line noise filters currently on the market is in the structure shown in FIG. 10. For a ferrite toroidal core 20 used for an inductor coil used in a broadband characteristic ferrite material that exhibits a large magnetic permeability value in the high-frequency region and an excellent low-loss characteristic. However, even though the ferrite material is a magnetic material that exhibits the excellent broadband characteristic, it is easily magnetic-saturated even with a small current value when used as an inductor. Thus, two coils 21, 22 are coiled around a single ferrite toroidal core 20 in many of the power-supply line noise filters on the market (e.g., Japanese Unexamined Patent Publication Hei 6-233521). They are coiled to mutually cancel magnetic flux φ within the ferrite toroidal core 20 as shown in FIG. 11 so that the ferrite toroidal core 20 does not lose the inductor function by being magnetically saturated with the normal mode power supply current of several to several tens of amperes flown in the power supply line. Thus, the two coils 21, 22 exhibit no inductor function for the normal-mode noise current and have no obstructing function thereof. However, for the common-mode noise current considered as a minute current that is so small that induces no magnetic saturation in the ferrite toroidal core 20 even when superimposed on the power supply line, the coils 21, 22 both function as the inductor since the directions of the magnetic flux φ become the same directions. That is, the two coils 21, 22 coiled around the ferrite toroidal core 20 are coils that are subjected to function to obstruct the common-mode noise current, and those are designed not to be magnetically saturated by the power supply current. In general, the coiled numbers of the coils 21, 22 are designed to be the same, and actually designed to obstruct the magnetic saturation regardless of the extent of the normal-mode power supply current value.
Patent Document 1: Japanese Unexamined Patent Publication Hei 6-233521
As described above, the inductor coil of the noise filter used for the conductor wire of the power supply line, for example, only has a function of preventing the common-mode noise current from flowing into the electronic device side but has no function of preventing the normal-mode noise current from flowing in. In the currently-used power-supply line noise filter of the basic structure shown in FIG. 10, the function of preventing the noise current of both of the normal and common modes from flowing into the electronic device side is designed to create a short-circuit state mainly by a capacitor C so that the noise frequency current does not flow into the electronic device side.
Next, a well-known and wide-spread noise countermeasure product using a ferrite material shown in FIG. 12 will be described. Noise countermeasure products of this type are put on the market from many ferrite material manufactures (TDK Corporation, NEC TOKIN Corporation, and the like). The noise countermeasure product is considered to exhibit a noise current reduction effect by inserting a conductor wire into an insertion hole 23a of a cylindrical ferrite core 23. Further, the noise countermeasure product shown in FIG. 13 is a developed type of the cylindrical ferrite noise countermeasure product shown in FIG. 12, and it is used by providing a plurality of insertion holes 24a in a plate-type ferrite core 24 in parallel and inserting a plurality of conductor wires thereto.
Regarding the noise countermeasure products using the ferrite shown in FIG. 12 and FIG. 13, it is assumed that the ferrite materials are so blended and sintering-processed that the loss of the magnetic substance is small in a low-frequency region that is a frequency region of a normal signal current flown in the conductor wire and that the loss of the magnetic substance is large in a high-frequency noise region that exceeds a signal frequency region. However, it is considered an extremely difficult task to adjust the noise current obstruction frequency region by blending the materials and executing a sintering work.
Further, a small current value is assumed as the signal current of the noise countermeasure products. Thus, those are employed for only the conductor wires that are not necessary to take the magnetic saturation of the ferrite material due to the current of the inserted conductor wire into consideration.
An object of the present invention is to provide a noise reducer which reduces the noise failure generated in the medical equipment and the computer-controlled electronic precision devices through consuming a part of the noise current superimposed on the conductor wires such as the power supply line and the earth line with the resistance provided on a winding-side circuit and suppressing the noise current superimposed on the conductor wires by electromagnetic induction between the conductor wires and the windings.